1. Field of the Invention
This invention relates to an ignition system for an internal combustion engine and more particularly to an ignition system including an arrangement for precluding the occurrence of reverse rotation running, particularly during starting of the engine.
2. Description of the Related Art
Spark ignited internal combustion engines generally include engine driven electrical generators for providing the electrical power to fire the ignition system. This may be done directly from the generator, as in the case of magneto ignition, of from the battery charging system of battery carrying machines. The timing of firing of the spark plug is controlled by a pulser coil that cooperates with a timing mark on the engine flywheel. These timing marks have a particular circumferential extent and generate positive and negative pulsed as the leading ad trailing ends pass the pulser coil.
To start the engine it is cranked in one of several manners. This cranking may be done by an electrical starter motor or manually by a kick starter, pull rope or crank, for example. The spark plug or plugs are then fired in response to a pulse signal from the pulser coil. However, at the time of original engine rotation the turning force applied may not be sufficient to resist the internal pressure generated in the combustion chamber. The internal pressure, if it overcomes the cranking force may cause the engine to rotate in a direction opposite to that desired. However the pulser coil will still create a pulse, in this instance from the trailing edge of the timing mark, and combustion will be initiated. Some engines, particularly two stroke ones can and will run in either direction. This presents significant problems both to the engine and its related equipment as well as to the starter and possibly even the operator.
A system has been proposed in Japanese Published Application Hei 9-151836 to avoid this problem. As disclosed in that application, in addition to the normal pulser coil and timing mark, a generator has at least two coil windings that output electrical energy as the engine rotates. These coil windings output sinusoidal wave outputs having positive and negative portions. The system includes a generator output polarity discriminating circuit which compares the polarity phase when the pulser coil is triggered and if the engine speed is below a predetermined value. From this the direction of crankshaft rotation is determined. If it is reversed from that desired, ignition is precluded.
The problem with this arrangement is that the timing mark must be located to register with the pole magnets of the generator to work. This compromises both the positioning and timing of the timing mark and the number of poles and coils in the generator.